ENH: improve vectorization of float comparisons

Unroll and use pack instructions instead of slowish movemask with lookup
table.
Doubles performance AMD phenoms and about 30% on Intel haswells.
Core2 also gain a few percent.
BUG: Fix deepcopy() of rank-zero arrays.

Removed call to PyArray_Return() on return value.

Closes #3311.
DOC: Remove extra reference (&) in PyArray_GetParamsFromObject example
Merge pull request #4431 from meltingwax/meltingwax/3311

BUG: Fix deepcopy() of rank-zero arrays.
Merge pull request #4432 from jaimefrio/getarrayparamsfromobj_doc

DOC: Remove extra reference (&) in PyArray_GetParamsFromObject example
Merge pull request #4429 from juliantaylor/bool-comp-improve

ENH: improve vectorization of float comparisons
DOC fix incorrect variable name in example

Undefined `dataaddr` -> `dataptrarray`
Merge pull request #4433 from jnothman/patch-4

DOC fix incorrect variable name in example